Generally, a high-voltage MOS transistor is a planar structure with an extended drain (MOS “drift”) so as to exhibit a high breakdown voltage.
For example, an MOS transistor with extended drain generally comprises an additional drain region called a “drift region” that has a lower density of dopants between the gate region and the normal drain region of the MOS transistor so as to avoid an excessively high electrical field upon an application of a high voltage between the gate and the drain of the MOS transistor.
However, since the gate dielectric layer of an MOS transistor with extended drain is generally uniform and thin, the end part of this dielectric layer situated in the vicinity of the drain always risks being broken down because of an electric field crowding phenomenon upon the application of a high voltage.
Moreover, an MOS transistor with planar extended drain is also costly in terms of surface footprint.